1. Field of the Invention
The invention relates to a flowmeter, which preferably operates using the Coriolis principle, having a guide structure that can have medium flowing through it.
2. Description of Related Art
Coriolis mass flowmeters are used primarily in industrial process measuring technology in such applications that require high measurement accuracies. The operation of Coriolis mass flowmeters is based on at least one measuring tube with a medium flowing through it—as part of a corresponding guide structure, which is traversed by said medium—being excited to oscillation by an oscillation generator. Due to the two speeds orthogonal to one another—that of the flow and that of the measuring tube—caused by the Coriolis inertial force, the medium having mass reacts with the wall of the measuring tube, whereby the oscillation of the measuring tube undergoes a change in comparison with an oscillation of the measuring tube without the flowing medium. By detecting the characteristic oscillations of the measuring tube with flow—as, in particular, the phase difference, and thus, the time difference between the deflection of two measuring tube sections that oscillate in-phase when the measuring tube has no flow—the mass flow through the measuring tube can be determined with greater accuracy. Therefore, Coriolis mass flowmeters are often used in applications requiring calibration.
In order to comply with such high accuracy requirements, the state of the Coriolis mass flowmeter must be accurately determined and variables influencing the measurement results in the calculation of the mass flow rate need to be considered. This includes information-bearing signals, i.e., the excitation signals (currents and/or voltages) and the primary measurement signals of interest—i.e., the deflections of the measuring tube—and also other influencing variables, such as the temperature or mechanical stresses at significant points of the measuring tube. These variables are then included in the calculation of the measured value, wherein model calculations or calibration data are used.
A measuring arrangement with voltage, length change or temperature sensors for correction of the measured values are described, for example, in German Patent Application DE 102 56 376 A1 and corresponding U.S. Pat. No. 6,868,740 B2 or German Patent DE 42 24 379 C1 and corresponding U.S. Pat. No. 5,381,697. The measuring tube detects its own oscillation using strain sensors according to the teaching of the patent U.S. Pat. No. 6,684,715 B1.
Coriolis mass flowmeters are suitable not only for determining a mass flow rate, but they can also be used, for example, for determining fluid density and viscosity of the medium, just as they are also suitable for the detection of diagnostic parameters, such as the detection of a multiphase flow or the detection of deposits. In view of these variables, there is a strong interest in a precise as possible, and above all, consistently precise detection of the measured values.
Difficulties in the use of measuring instruments in process automation are often caused by cramped space, which make it necessary that the measuring instruments are as small as possible and designed in a compact manner.